Studies will be carried out to gain an understanding of the physiologic role of placental thyrotropins in the control of thyroid function during pregnancy. A more sensitive radioimmunoassay will be developed for chorionic thyrotropin. Thyroid-stimulating activity will be measured at monthly intervals during pregnancy using a more sensitive mouse bioassay. The results will be compared with radioimmunoassays of serum pituitary TSH, chorionic thyrotropin (hCT), chorionic gonadotropin (hCG), T4, T3, free T4 and free T3. The thyroid-stimulating activity of hCg will be tested in experimental animals. The effect of hypothalamic releasing factors on the secretion of hCT and hCG by placental tissue will be tested in a perfusion system. BIBLIOGRAPHIC REFERENCES: Drenick, E.J., Carlson, H.E., Hershman, J.M., and Robertson, G.L. The role of vasopressin and prolactin in abnormal salt and water metabolism of obese patients before and after fasting and during refeeding. Metabolism 26: 1977. Granoff, A.B., and Hershman, J.M. Suppression of pituitary TSH in a child with a hyperfunctioning thyroid nodule. J. Pediatrics 90:83-85, 1977.